There is a considerable body of empirical evidence suggesting that point-of-sale tobacco (POST) marketing influences tobacco users' product preferences as well as decisions to initiate or refrain from use. Yet little is known about the mechanisms that underlie the association between point-of-sale marketing and behavior, because methods that directly link individual use outcomes to real-world point-of-sale exposure are only now beginning to be developed. There is an urgent need for data to fill this research gap, as the inability to empirically document a direct link between POST exposure and behavior is among the primary reasons proposed point-of-sale regulations have often failed to withstand industry legal challenge. The proposed project will provide data to directly address this critical knowledge gap. It extends the use of an innovative methodology that has been the first to provide objective, real-time data on the degree to which individuals are exposed to point-of-sale marketing as they move through their daily activities, as well as the way accumulating exposure to marketing affects use patterns over time. Quantifying real-time point-of-sale tobacco exposure (POSTE) requires a multilevel system with both comprehensive point-of-sale data at the community level and location-based exposure data at the individual level. Because it is impossible to predict where each individual will travel from moment-to-moment, characterizing their point-of-sale experience must begin with comprehensive data on marketing in each person's immediate environment. The POSTE system includes two key components: 1) community-level data collection by fieldworkers, and 2) individual-level geo- location data. Unlike other approaches, POSTE measurement does not require active input from participants and thus is not subjective. Entirely separate from community-level point-of-sale data collected via fieldworkers, POSTE participants consent to continuous location tracking. Data are wirelessly synced to a secure server, where advanced geographic information system (GIS) infrastructure links each person to their point-of-sale environment in real-time. Thus, detailed POSTE data is accurately quantified with very low participant burden. The proposed project couples our existing point-of-sale surveillance system with continuous (1-min sampling rate) geo-spatial exposure data from current DC resident tobacco users. The Washington DC metropolitan area provides an ideal community-level laboratory for this purpose, because 1) DC is characterized by tremendous demographic variation over a small geographic area, making it possible to evaluate socio-economic correlates of POST marketing at every tobacco outlet in DC quickly and repeatedly, 2) DC is a focus city for tobacco industry marketing, and 3) we have an existing DC resident smoker cohort that can readily be engaged and replenished. Participants (N=1200) will be current cigarette smokers not currently interested in quitting. All participants will be offered the opportunity to be compensated and to learn more about their exposure to tobacco marketing by carrying a geolocation tracking device for two-weeks at baseline and then again as part of each quarterly assessment. This will create a physical link between each person and their surrounding POST marketing environment. Quarterly follow-up assessments will assess subjectively perceived levels of POSTE and tobacco-use patterns across the study period. The proposed project represents a powerful new approach to understand and thereby combat the way POST marketing tactics affect tobacco use patterns. The project will provide data and tools for real-time analysis of POST marketing regulations and tobacco use, iteratively improving both policy and enforcement standards by linking them directly to the behavioral outcomes they are designed to affect.